document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=341457>Question 341457</A>: <I><SPAN STYLE=\"word-break: break-all;\"> The decay rate of iodine-131<BR>\n" );
document.write( "is 9.6% per day. What is its half-life? </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #244542 by </B><A HREF=/tutors/aboutme.mpl?userid=Alan3354><B>Alan3354(69443)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=Alan3354><IMG SRC=http://www.algebra.com/images/aboutme-small.gif BORDER=0 alt=\"About Me\" VALIGN=MIDDLE></A>&nbsp;<IMG SRC=http://www.algebra.com/cgi-bin/show-face.mpl?user=Alan3354><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=244542\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> The decay rate of iodine-131<BR>\n" );
document.write( "is 9.6% per day. What is its half-life?<BR>\n" );
document.write( "----------------<BR>\n" );
document.write( "At the end of each day, 90.4% is left (100 - 9.6) = 0.904 of the day before.<BR>\n" );
document.write( "0.5 = 0.904^t (t in days)<BR>\n" );
document.write( "ln(0.5) = t*ln(0.904)<BR>\n" );
document.write( "t = ln(0.5)/ln(0.904)<BR>\n" );
document.write( "t =~ 6.868 days<BR>\n" );
document.write( "------------------<BR>\n" );
document.write( "You could use log instead of ln, the results are the same.\r<BR>\n" );
document.write( "\n" );
document.write( " </SPAN>\n" );
document.write( "</TD></TR></TABLE>\n" );